Thursday, 20 March 2014

Hoover cannon ...

For some time I've wanted to make a hoover cannon, and show the kids on some level at least a little bit about air pressure, a hoover cannon is great for this because they're fun and easy to make.

We actually made three different cannons, from stuff we had lying about the house, two are made from various bits of plastic pipe, and the third we made out of cardboard, which I have to be honest I didn't think was going to work.

Here they are -

Easy enough to make, especially the large white one.

They are all built the same way, a large tube for the projectile and a smaller tube to connect the hoover to, the bit on the end is basically a valve (it needs some tweaking as you'll see from the video) you don't need to make a valve, a bit of paper on the end is enough to achieve the same result.

As you can see the largest cannon is made from plastic pipe, with a fitting, it's all push together, so there's no gluing needed, I had the pipe already, and the fitting cost me about £2.00, the other two cannons are held together with black insulation tape, all I did was to cut a hole in the main tube to allow the air to flow, and that's about it.

Plenty of tape is best -

The tape helps stop leaks as well as hold it all together.

The valve (burst disc) is a piece of thin plastic taped to a bit of thin plywood, which I cut a hole in and then glued to the end of each cannon, obviously there are three different sized ones, but they all work the same way, that being to seal the hole and then move when the projectile hits them.

The valve (burst disc) -

The clear plastic is from the front of a box a toy came in.

We made a few different projectiles to fit the various cannons we also tried making them heavier to see if that affected how far they went, you can use various different things, tin foil screwed into a ball, old film cases, the plastic things from kinder eggs, wood, basically anything that will fit down the tube without getting stuck.

Some of our projectiles -

I wrote on them so we could remember what weights we had.

Here's a simple diagram of how it all works, but there are numerous articles online on how to make these, and how they work, and there is a supersonic version of this that fires a ping pong ball at mach 1.2 (about 912 mph)

Diagram -

A simple diagram.

Plastic tube is best, but you can use cardboard tubes as long as they are very strong ones, the sort that tin foil or cling film comes on, or the tubes you can get to post posters and the like, toilet rolls probably won't work.

Here's a video of ours in action, you can see I need to work on the valve / burst disc set up, they weren't meant to fly off the ends of the cannons, and we should have really added some kind of trigger set up to make it easier to load and fire the cannons, we may make changes to them at a later date.